1. Field of the Invention
The present invention relates to a switching regulator.
2. Description of the Related Art
Power requirements of portable electronic devices such as mobile phones and Personal Digital Assistants (PDAs) are sometimes higher or lower in terms of voltage than that supplied by the battery. In order to supply a proper voltage, a buck or boost-buck switching regulator (DC/DC converter) is commonly employed.
Lag control has come to replace pulse width modulation and pulse frequency modulation control method employed by the switching element of a switching regulator. FIG. 1 shows a circuit diagram of a buck switching regulator using lag control. A switching regulator 1004 includes switching transistors M1, M2 (M2 is also called as synchronous rectified transistor), inductor L1, output capacitor C1 and control circuit 1100.
The resistors R1, R2 are used to divide the output voltage VOUT. The divided output voltage VOUT′ is input to a reverse input terminal (−) of a lag comparator 22. The lag comparator 22 is used to compare the voltage VFB of the reverse input terminal with reference voltage VREF of the non-reverse input terminal, and to generate a pulse signal S1 representing a compared result. According to the pulse signal S1, a driver 20 is used to switch the switching transistor M1 and the synchronous rectified transistor M2 using complementary method. A switching voltage VLX of a connecting point connecting the switching transistor M1 and the synchronous rectified transistor M2 feeds back to the reverse input terminal of the lag comparator 22 through a feedback circuit 24 having a feedback resistor RFB and a feedback capacitor CFB. That is, the feedback voltage VFB of the reverse input terminal of the lag comparator 22 overlaps a DC component VOUT′ of output voltage VOUT and the switching voltage VLX.